A gas spring of this type with a surrounding tube is known from German patent 28 49 267 or published German patent application 32 25 974. The purpose of this surrounding tube is to provide an additional regulating length. This may be, for example, the case when an engine bonnet of a motor vehicle is to be movable by means of the gas spring to a central open position. On the other hand, it may be desirable for more extensive work on the engine or the like to open the bonnet beyond an open slanting position. In this instance the surrounding tube is then partly or fully pulled out from the housing of the gas spring, the bonnet being then opened beyond its top dead centre. To prevent an inadvertent pulling out of the surrounding tube from the housing of the gas spring it has in practice already become known to provide a device for locking the housing of the gas spring with the surrounding tube in the fully pushed in end position of the housing. This device consists in a spring buckle clamped externally on the surrounding tube, having a locking portion which, in this end position of the housing in the surrounding tube, as a consequence of the elastic tensioning of the spring buckle, clamps in front of the front side of the housing. To pull out the housing from the surrounding tube, the locking portion is pivoted out against the tensioning of the buckle out of the surrounding tube transversely to the central longitudinal axis of the gas spring. This known construction assumes that the part supported by the gas spring, for example, therefore, the engine bonnet, supports itself or finds itself in a stable position.